--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_e2e_policy/mod_e2e_policy.lua	Tue Jun 14 18:03:05 2016 +0200
@@ -0,0 +1,54 @@
+local st = require "util.stanza";
+local host = module.host;
+local e2e_policy_chat = module:get_option_string("e2e_policy_chat", "optional"); -- possible values: none, optional and required
+local e2e_policy_muc = module:get_option_string("e2e_policy_muc", "optional"); -- possible values: none, optional and required
+local e2e_policy_whitelist = module:get_option_set("e2e_policy_whitelist", {  }); -- make this module ignore messages sent to and from this JIDs or MUCs
+
+local e2e_policy_message_optional_chat = module:get_option_string("e2e_policy_message_optional_chat", "For security reasons, OMEMO, OTR or PGP encryption is STRONGLY recommended for conversations on this server.");
+local e2e_policy_message_required_chat = module:get_option_string("e2e_policy_message_required_chat", "For security reasons, OMEMO, OTR or PGP encryption is required for conversations on this server.");
+local e2e_policy_message_optional_muc = module:get_option_string("e2e_policy_message_optional_muc", "For security reasons, OMEMO, OTR or PGP encryption is STRONGLY recommended for MUC on this server.");
+local e2e_policy_message_required_muc = module:get_option_string("e2e_policy_message_required_muc", "For security reasons, OMEMO, OTR or PGP encryption is required for MUC on this server.");
+
+function warn_on_plaintext_messages(event)
+    if e2e_policy_whitelist:contains(event.stanza.attr.from) or e2e_policy_whitelist:contains(event.stanza.attr.to) then -- check if JID is whitelisted
+        return nil;
+    end
+    local body = event.stanza:get_child_text("body");
+    -- do not warn for status messages
+    if not body then
+        return nil;
+    end
+    -- check otr
+    if body and body:sub(1,4) == "?OTR" then
+        return nil;
+    end
+    -- check omemo https://xmpp.org/extensions/inbox/omemo.html
+    if event.stanza:get_child("encrypted", "eu.siacs.conversations.axolotl") or event.stanza:get_child("encrypted", "urn:xmpp:omemo:0") then
+        return nil;
+    end
+    -- check xep27 pgp https://xmpp.org/extensions/xep-0027.html
+    if event.stanza:get_child("x", "jabber:x:encrypted") then
+        return nil;
+    end
+	-- check xep373 pgp (OX) https://xmpp.org/extensions/xep-0373.html
+    if event.stanza:get_child("openpgp", "urn:xmpp:openpgp:0") then
+        return nil;
+    end
+    -- no valid encryption found
+    if e2e_policy_chat == "optional" and event.stanza.attr.type ~= "groupchat" then
+        event.origin.send(st.message({ from = host, type = "headline" }, e2e_policy_message_optional_chat));
+    end
+    if e2e_policy_chat == "required" and event.stanza.attr.type ~= "groupchat" then
+        return event.origin.send(st.error_reply(event.stanza, "modify", "policy-violation", e2e_policy_message_required_chat));
+    end
+    if e2e_policy_muc == "optional" and event.stanza.attr.type == "groupchat" then
+        event.origin.send(st.message({ from = host, type = "headline" }, e2e_policy_message_optional_muc));
+    end
+    if e2e_policy_muc == "required" and event.stanza.attr.type == "groupchat" then
+        return event.origin.send(st.error_reply(event.stanza, "modify", "policy-violation", e2e_policy_message_required_muc));
+    end
+end
+
+module:hook("pre-message/bare", warn_on_plaintext_messages, 300);
+module:hook("pre-message/full", warn_on_plaintext_messages, 300);
+module:hook("pre-message/host", warn_on_plaintext_messages, 300);